An abrasion-resistant material which is stable even in an oxidizing atmosphere of above 500.degree. C is needful for articles subject to movement in such atmosphere, typified by a rotary regenerator in a gas turbine, as the material of a seal layer or a lubricating layer which provides a rubbing contact face.
At present, an abrasion-resistant layer for such purpose is usually produced by coating a surface of a metal substrate such as a stainless steel sheet with a plasma-sprayed mixture of a heavy metal oxide such as nickel oxide or cobalt oxide and a solid lubricating material typified by calcium fluoride. A coating of this type is desired to have a sufficiently large thickness for acquiring a long life and protecting the substrate against corrosion and temperature rise. However, it is difficult to make the thickness more than about 1 mm because, as the coating is formed to a larger thickness, a separation into two layers tends to occur in the coating due to thermal stress during a spraying process. Besides, an abrasion-resistant layer of this type is rather susceptible to heat shocks, probably because of a difference in thermal expansion coefficient between the substrate material and the coated material, and tends to exhibit a separation from the substrate or an undercoat layer during use.
Sometime, an abrasion-resistant layer or board is produced by sintering a powder mixture of the above described heavy metal oxide and solid lubricating material. However, a great difference of the melting point of the solid lubricating material (about 1300.degree.-1400.degree. C) from that of the heavy metal oxide (about 1800.degree.-2000.degree. C) offers a significant problem to the sintering. The sintering temperature should be as high as about 1600.degree.-1800.degree. C to realize a fully sintered structure, but the solid lubricant completely melts at such high temperature and develops a considerable quantity of gas, resulting in an undesirably great porosity and fragility of the sintered product. Besides, an inherently poor formability of the material (as a property common to ceramics, the described material in the form of a board breaks without undergoing plastic deformation) also leads to an insufficient toughness and wear resistance of the sintered product.